The field of the present invention relates to the delivery of energy impulses (and/or fields) to bodily tissues for therapeutic purposes, for example, for treating medical conditions such as migraine headaches. The energy impulses (and/or fields) that are used to treat such conditions comprise electrical and/or electromagnetic energy, delivered non-invasively to the patient, particularly to a vagus nerve of the patient. During the course of such treatment, a caregiver and/or the patient uses the disclosed devices and methods to monitor whether the treatment is being applied safely and effectively.
The use of electrical stimulation for treatment of medical conditions is well known. One of the most successful applications of modern understanding of the electrophysiological relationship between muscle and nerves is the cardiac pacemaker. Although origins of the cardiac pacemaker extend back into the 1800's, it was not until 1950 that the first practical, albeit external and bulky, pacemaker was developed. The first truly functional, wearable pacemaker appeared in 1957, and in 1960, the first fully implantable pacemaker was developed.
Around this time, it was also found that electrical leads could be connected to the heart through veins, which eliminated the need to open the chest cavity and attach the lead to the heart wall. In 1975 the introduction of the lithium-iodide battery prolonged the battery life of a pacemaker from a few months to more than a decade. The modern pacemaker can treat a variety of different signaling pathologies in the cardiac muscle, and can serve as a defibrillator as well (see U.S. Pat. No. 6,738,667 to DENO, et al., the disclosure of which is incorporated herein by reference). Because the leads are implanted within the patient, the pacemaker is an example of an implantable medical device.
Another such example is electrical stimulation of the brain with implanted electrodes (deep brain stimulation), which has been approved for use in the treatment of various conditions, including pain and movement disorders such as essential tremor and Parkinson's disease [Joel S. PERLMUTTER and Jonathan W. Mink. Deep brain stimulation. Annu. Rev. Neurosci 29 (2006):229-257].
Another application of electrical stimulation of nerves is the treatment of radiating pain in the lower extremities by stimulating the sacral nerve roots at the bottom of the spinal cord [Paul F. WHITE, shitong Li and Jen W. Chiu. Electroanalgesia: Its Role in Acute and Chronic Pain Management. Anesth Analg 92 (2001):505-513; U.S. Pat. No. 6,871,099, entitled Fully implantable microstimulator for spinal cord stimulation as a therapy for chronic pain, to WHITEHURST, et al].
The form of electrical stimulation that is most relevant to the present invention is vagus nerve stimulation (VNS, also known as vagal nerve stimulation). It was developed initially for the treatment of partial onset epilepsy and was subsequently developed for the treatment of depression and other disorders. The left vagus nerve is ordinarily stimulated at a location within the neck by first surgically implanting an electrode there and then connecting the electrode to an electrical stimulator [U.S. Pat. No. 4,702,254 entitled Neurocybernetic prosthesis, to ZABARA; U.S. Pat. No. 6,341,236 entitled Vagal nerve stimulation techniques for treatment of epileptic seizures, to OSORIO et al; U.S. Pat. No. 5,299,569 entitled Treatment of neuropsychiatric disorders by nerve stimulation, to WERNICKE et al; G. C. ALBERT, C. M. Cook, F. S. Prato, A. W. Thomas. Deep brain stimulation, vagal nerve stimulation and transcranial stimulation: An overview of stimulation parameters and neurotransmitter release. Neuroscience and Biobehavioral Reviews 33 (2009):1042-1060; GROVES D A, Brown V J. Vagal nerve stimulation: a review of its applications and potential mechanisms that mediate its clinical effects. Neurosci Biobehav Rev 29 (2005):493-500; Reese TERRY, Jr. Vagus nerve stimulation: a proven therapy for treatment of epilepsy strives to improve efficacy and expand applications. Conf Proc IEEE Eng Med Biol Soc. 2009; 2009:4631-4634; Timothy B. MAPSTONE. Vagus nerve stimulation: current concepts. Neurosurg Focus 25 (3, 2008):E9, pp. 1-4; ANDREWS, R. J. Neuromodulation. I. Techniques-deep brain stimulation, vagus nerve stimulation, and transcranial magnetic stimulation. Ann. N.Y. Acad. Sci. 993 (2003):1-13; LABINER, D. M., Ahern, G. L. Vagus nerve stimulation therapy in depression and epilepsy: therapeutic parameter settings. Acta. Neurol. Scand. 115 (2007):23-33; AMAR, A. P., Levy, M. L., Liu, C. Y., Apuzzo, M. L. J. Vagus nerve stimulation. Proceedings of the IEEE 96(7, 2008)1142-1151].
Many such therapeutic applications of electrical stimulation involve the surgical implantation of electrodes within a patient. In contrast, devices used for the procedures that are disclosed here do not involve surgery, i.e., they are not implantable medical devices. Instead, the present devices and methods stimulate nerves by transmitting energy to nerves and tissue non-invasively. A medical procedure is defined as being non-invasive when no break in the skin (or other surface of the body, such as a wound bed) is created through use of the method, and when there is no contact with an internal body cavity beyond a body orifice (e.g., beyond the mouth or beyond the external auditory meatus of the ear). Such non-invasive procedures are distinguished from invasive procedures (including minimally invasive procedures) in that the invasive procedures insert a substance or device into or through the skin (or other surface of the body, such as a wound bed) or into an internal body cavity beyond a body orifice.
For example, transcutaneous electrical stimulation of a nerve is non-invasive because it involves attaching electrodes to the skin, or otherwise stimulating at or beyond the surface of the skin or using a form-fitting conductive garment, without breaking the skin [Thierry KELLER and Andreas Kuhn. Electrodes for transcutaneous (surface) electrical stimulation. Journal of Automatic Control, University of Belgrade 18(2, 2008):35-45; Mark R. PRAUSNITZ. The effects of electric current applied to skin: A review for transdermal drug delivery. Advanced Drug Delivery Reviews 18 (1996) 395-425]. In contrast, percutaneous electrical stimulation of a nerve is minimally invasive because it involves the introduction of an electrode under the skin, via needle-puncture of the skin.
Another form of non-invasive electrical stimulation is magnetic stimulation. It involves the induction, by a time-varying magnetic field, of electrical fields and current within tissue, in accordance with Faraday's law of induction. Magnetic stimulation is non-invasive because the magnetic field is produced by passing a time-varying current through a coil positioned outside the body. An electric field is induced at a distance, causing electric current to flow within electrically conducting bodily tissue. The electrical circuits for magnetic stimulators are generally complex and expensive and use a high current impulse generator that may produce discharge currents of 5,000 amps or more, which is passed through the stimulator coil to produce a magnetic pulse. The principles of electrical nerve stimulation using a magnetic stimulator, along with descriptions of medical applications of magnetic stimulation, are reviewed in: Chris HOVEY and Reza Jalinous, The Guide to Magnetic Stimulation, The Magstim Company Ltd, Spring Gardens, Whitland, Carmarthenshire, SA34 0HR, United Kingdom, 2006. In contrast, the magnetic stimulators that have been disclosed by the present Applicant are relatively simpler devices that use considerably smaller currents within the stimulator coils. Accordingly, they are intended to satisfy the need for simple-to-use and less expensive non-invasive magnetic stimulation devices.
Potential advantages of such non-invasive medical methods and devices relative to comparable invasive procedures are as follows. The patient may be more psychologically prepared to experience a procedure that is non-invasive and may therefore be more cooperative, resulting in a better outcome. Non-invasive procedures may avoid damage of biological tissues, such as that due to bleeding, infection, skin or internal organ injury, blood vessel injury, and vein or lung blood clotting. Non-invasive procedures are generally painless and may be performed without the dangers and costs of surgery. They are ordinarily performed even without the need for local anesthesia. Less training may be required for use of non-invasive procedures by medical professionals. In view of the reduced risk ordinarily associated with non-invasive procedures, some such procedures may be suitable for use by the patient or family members at home or by first-responders at home or at a workplace. Furthermore, the cost of non-invasive procedures may be significantly reduced relative to comparable invasive procedures.
In co-pending, commonly assigned patent applications, Applicant disclosed noninvasive electrical and magnetic vagus nerve stimulation devices, which are adapted, and for certain applications improved, in the present disclosure [application Ser. No. 13/183,765 and Publication US2011/0276112, entitled Devices and methods for non-invasive capacitive electrical stimulation and their use for vagus nerve stimulation on the neck of a patient, to SIMON et al.; Application 12/964,050 and Publication US2011/0125203, entitled Magnetic Stimulation Devices and Methods of Therapy, to SIMON et al.; and other co-pending commonly assigned applications that are cited herein, which are incorporated by reference]. The present disclosure elaborates on the electrical stimulation device, rather than the magnetic stimulation device that has similar functionality, with the understanding that unless it is otherwise indicated, the elaboration could apply to either the electrical or the magnetic nerve stimulation device.
The non-invasive nerve stimulator may be applied to the patient by a trained healthcare provider or by the patient himself or herself, after having been evaluated and trained in its use by the healthcare provider. The primary advantage of the self-stimulation therapy is that it can be administered more or less immediately when symptoms occur, rather than having to visit the healthcare provider at a clinic or emergency room. The need for such a visit would only compound the aggravation that the patient is already experiencing. Another advantage of the self-stimulation therapy is the convenience of providing the therapy in the patient's home or workplace, which eliminates scheduling difficulties, for example, when the nerve stimulation is being administered for prophylactic reasons at odd hours of the day. Furthermore, the cost of the treatment may be reduced by not requiring the involvement of a trained healthcare provider.
However, a disadvantage of having patients apply the therapy to themselves is that the patient may not always perform the therapy in an optimal fashion, despite having been trained by the caregiver to do so. Furthermore, individual patients may vary in their responsiveness to the therapy, even if it is performed in an optimal fashion. Even the same patient may exhibit day-to-day variations in responsiveness to the therapy. Accordingly, there is need in the art for devices and methods that aid the caregiver and the patient in assuring that the therapy is being administered in an optimal fashion, such that the therapy will be maximally effective and yet have minimum undesirable side-effects. In particular, there is a need for methods to assure that the stimulation is always being performed at an optimal anatomical location on the patient, that the therapy is unambiguously stimulating the target nerve (e.g., vagus nerve), and that the level of stimulation is therapeutically appropriate, as explained in more detail below.
Electrical stimulation by the disclosed methods and devices may be used to treat many medical conditions, including the conditions that are described in the cited co-pending, commonly assigned patent applications. An exemplary teaching of the present invention is the treatment of migraine and other primary headaches such as cluster headaches, including sinus symptoms (“sinus” headaches) irrespective of whether those symptoms arise from an allergy that is co-morbid with the headache. Background information concerning the treatment of migraine headaches by noninvasive vagus nerve stimulation will now be summarized. For more detailed background information on the use of such stimulation to treat migraine/sinus headaches, please refer to co-pending, commonly assigned application number U.S. Ser. No. 13/109,250 with publication number US20110230701, entitled Electrical and magnetic stimulators used to treat migraine/sinus headache and comorbid disorders to SIMON et al; and application number U.S. Ser. No. 13/183,721 with publication number US20110276107, entitled Electrical and magnetic stimulators used to treat migraine/sinus headache, rhinitis, sinusitis, rhinosinusitis, and comorbid disorders, to SIMON et al, which are incorporated by reference.
Chronic daily headache by definition occurs with a frequency of at least 15 headache days per month for greater than 3 months duration. Chronic migraine sufferers comprise a subset of the population of chronic headache sufferers, as do those who suffer other primary headache disorders such as chronic tension-type headache [Bert B. VARGAS, David W. Dodick. The Face of Chronic Migraine: Epidemiology, Demographics, and Treatment Strategies. Neurol Clin 27 (2009) 467-479; Peter J. GOADSBY, Richard B. Lipton, Michel D. Ferrari. Migraine—Current understanding and treatment. N Engl J Med 346 (4, 2002): 257-270; Stephen D SILBERSTEIN. Migraine. LANCET 363 (2004):381-391].
A migraine headache typically passes through the following stages: prodromal, aura, headache pain, and postdromal. All these phases do not necessarily occur, and there is not necessarily a distinct onset or end of each stage, with the possible exception of the aura. An interictal period follows the postdromal, unless the postrome of one migraine attack overlaps the prodrome of the next migraine attack.
The prodrome stage comprises triggering events followed by premonitory symptoms. The prodrome is often characterized by fatigue, sleepiness, elation, food cravings, depression, and irritability, among other symptoms. Triggers (also called precipitating factors) such as excessive stress or sensory barrage usually precede the attack by less than 48 h. The average duration of the prodrome is 6 to 10 hours, but in half of migraine attacks, the prodrome is less than two hours (or absent), and in approximately 15% of migraine attacks, the prodrome lasts for 12 hours to 2 days.
The aura is due to cortical spreading depression within the brain. Approximately 20-30% of migraine sufferers experience an aura, ordinarily a visual aura, which is perceived by the patient as a scintillating scotoma (zig-zag line) that moves within the patient's visual field for typically half an hour. However, aura symptoms, regardless of their form, vary to a great extent in duration and severity from patient to patient, and also within the same individual.
Although the headache phase can begin at any hour, it most commonly begins as mild pain when the patient awakens in the morning. It then gradually builds at variable rates to reach a peak at which the pain is usually described as moderate to severe. Migraine headaches often occur on both sides of the head in children, but an adult pattern of unilateral pain often emerges in adolescence. The pain is often reported as starting in the occipital/neck regions, later becoming frontotemporal. It is throbbing and aggravated by physical effort, with all stimuli tending to accentuate the headache. The pain phase lasts 4-72 h in adults and 1-72 h in children, with a mean duration generally of less than 1 day. The pain intensity usually follows a smooth curve with a crescendo with a diminuendo. After the headache has resolved, many patients are left with a postdrome that lingers for one to two days. The main complaints during the prodrome are cognitive difficulties, such as mental tiredness.
For the present medical applications, an electrical stimulator device is ordinarily applied to the patient's neck. In a preferred embodiment of the invention, the stimulator comprises two electrodes that lie side-by-side within separate stimulator heads, wherein the electrodes are separated by electrically insulating material. Each electrode and the patient's skin are connected electrically through an electrically conducting medium that extends from the skin to the electrode. The level of stimulation power may be adjusted with a wheel or other control feature that also serves as an on/off switch.
The position and angular orientation of the device are adjusted about a location on the neck until the patient perceives stimulation when current is passed through the stimulator electrodes. An objective of the present invention is to assure that the position of the stimulator on the neck is therapeutically optimal. The following related issue also arises. Although the stimulator is designed to be robust against very small variations in position of the stimulator relative to the vagus nerve, fluctuating movement of the stimulator relative to the nerve being stimulated is to some extent unavoidable, due for example to neck muscle contractions that accompany breathing. Such unavoidable movement of the device makes it difficult to assure that the patient is receiving exactly the prescribed stimulation dose in each stimulation session. Accordingly, an objective of the invention is to measure such movement and compensate for it.
The applied current is then increased gradually, first to a level wherein the patient feels sensation from the stimulation. The power is then further increased, but is set to a level that is less than one at which the patient first indicates any discomfort. Another objective of the present invention is to assure that the target nerve (e.g. vagus nerve) is being stimulated, such that the sensation that the patient experiences is not simply due to electrical current passing through the skin and muscle beneath the stimulator heads.
The electrical stimulation is then typically applied for 5 to 30 minutes, which is often sufficient to at least partially relieve headache pain within 5 minutes. The treatment then causes patients to experience a very rapid relief from headache pain, as well as a rapid opening of the nasal passages within approximately 20 minutes. Effects of the treatment may last for 4 to 5 hours or longer. However, for some patients the stimulation is performed for prophylactic purposes, i.e., to prevent a headache from occurring, such that the patient cannot use prompt relief of headache pain as an indication of whether the stimulation was being performed optimally. Furthermore, when the patient is being instructed in the use of the stimulator by a caregiver, such instruction may take place when no headache is in progress. Accordingly, another objective of the present invention is to assure that the stimulation parameters are being set in an optimal fashion during a therapeutic session, without necessarily relying on the prompt relief of symptoms as a guide for whether the parameter selection was appropriate (e.g., selection of stimulation amplitude).
Despite the advantages of having a patient administer the nerve stimulation by himself or herself, such self-stimulation also presents certain risks and difficulties relating to safety. In some situations, the vagus nerve stimulator should be applied to the left or to the right vagus nerve, but not vice versa. In some situations, it would be beneficial to apply the stimulator to both sides of the neck in a prescribed order. On the other hand, in some situations the stimulation may actually be most beneficial if applied to the right vagus nerve, and it may be relatively less effective if applied to the left vagus nerve. Therefore, if the patient is using the vagus nerve stimulator by himself or herself, it would be useful for the device be designed so that it can be used only on the prescribed side of the neck. The present invention discloses several methods for preventing inadvertent stimulation on the side of the neck that is not prescribed.
Another problem is that the patient may wish to stop the stimulation session based only on some subjective assessment of whether the stimulation has sufficiently relieved the symptoms. However, there may be a diminishing effectiveness if the stimulation session is too long, for the following reason. Let the numerical value of the accumulated effects of vagus nerve stimulation be denoted as S(t). It may for present exemplary purposes be represented as a function that increases at a rate proportional to the stimulation voltage V in the vicinity of the nerve and decays with a time constant τP, such that after prolonged stimulation, the accumulated stimulation effectiveness may saturate at a value equal to the product of V and τP. Thus, if TP is the duration of a vagus nerve stimulation in a particular treatment session, then for time t<TP, S(t)=Vτ[1−exp(−t/τP)]+S0 exp(−t/τP),
and for t>TP, S(t)=S(TP) exp (−[t−TP]/τP), where the time t is measured from the start of a stimulus, and S0 is the value of S when t=0. The optimal duration of a stimulation session may be different from patient to patient, because the decay time constant τP may vary from patient to patient. To the extent that the stimulation protocol is designed to treat each patient individually, such that subsequent treatment sessions are designed in view of the effectiveness of previous treatment sessions, it is would be useful for the stimulation amplitude V be as constant as possible, and the treatment session should take into account the above-mentioned principle of diminishing returns. At a minimum, the average stimulation amplitude in a session should be estimated or evaluated, despite movement of the stimulator relative to the nerve and despite any amplitude adjustment by the patient. The present invention discloses methods and devices for doing so.